A recent study examined the value of gene sequencing in cancer in order to determine what drugs might be effective (1). Some of the findings, comparing results obtained from two sequencing companies, Foundation1 (F1) and Guardant (G360), were rather startling. The percentage of mutations detected by both platforms varied from 21 to 58%, not even approaching 100%, which would of course mean that the results agreed, no matter which company was used. In only a single case out of the 9 patients studied did both platforms detect all of the known mutations (changes in the gene sequence), while in the rest of the cases the 2 platforms hovered around detection of 25% of the mutations.The 2 platforms were also compared in terms of which drug therapies they recommended for the 9 patients in the study. In only 2 cases did both platforms recommend the same drugs, while for an astounding 6 out of 9 cases, there was no agreement at all between the 2 platforms.These results are very concerning because these tests, and those offered by a number of other companies, are performed on many thousands of patients every year at considerable cost.One caveat to this study is that the two testing platforms did not use the same materials. The F1 test used tumor tissue from the patients, whereas the G360 test used circulating tumor cell DNA obtained from the blood (so-called liquid biopsy). Therefore, the results may reflect, to a certain extent, what is called heterogeneity in the cancers, a subject that will be the topic of future posts.The expensive results generated by these sorts of tests may well be misleading, if not downright meaningless.Therefore, of what use is precision medicine if it offers nothing that is clinically useful?